Semiconductor automatic test equipment (ATE) is used in semiconductor manufacturing processes to perform electrical testing and/or characterization of semiconductor devices. The semiconductor device being tested is usually referred to as the Device Under Test (DUT). FIG. 1 is a schematic diagram of a conventional semiconductor ATE. Referring to FIG. 1, an ATE 10, or a “tester,” generally includes multiple programmable power supplies, such as Supply-1 to Supply-N, under the control of a controller 15. The controller 15 directs one or more power supplies to apply certain stimuli to the device under test (DUT) 20 and also to measure or detect responses from the DUT 20. In particular, each power supply is configured to provide a driving voltage and a driving current within a given specified range, such as up to 20V and 20 mA. Each power supply has an output terminal 18 coupled to a pin of the DUT 20. The pin can be an input pin, an output pin, or an input-output pin.
Some semiconductor devices require high current or high voltage in certain modes of operation. One limitation of low cost ATE is the lack of sufficient programmable high power (>20 mA) voltage sources which limits the tester's ability to test semiconductor devices that operate at high voltage and/or high current level. Commercially available ATEs that include one or more high voltage or high current power supplies are typically very costly. Furthermore, these expensive ATEs typically include only a limited number of high voltage/high current power supplies, which is often not sufficient for testing some semiconductor devices or for testing multiple devices simultaneously. Some attempts to provide a high current/voltage power supply in a tester include using an amplifier to amplify the voltage and current at the output terminal of the low voltage power supply. However, insertion of such amplifier into the connection between the power supply and the DUT breaks the sense connection of the tester and prevents the tester from sensing or detecting the signal level at the DUT pin.
FIG. 2 is a schematic diagram of the force/sense connection between a power supply on a tester and a pin of the DUT. Referring to FIG. 2, the output terminal of a power supply Supply-K in a tester includes a force line (node 28) and a sense line (node 29) that are Kelvin connected to a pin in the DUT 20. The force line and sense line are sometimes referred to as a force-and-sense pair. The force and sense lines are connected together at the DUT pin to form a Kelvin connection. In a Kelvin connection, the power supply Supply-K supplies current via the force line (node 28) and the voltage at the DUT pin is sensed by the sense line (node 29) while no current flows in the sense line. The power supply Supply-K forces a programmed voltage VSK (e.g., 5V) onto the force line at a given current level and senses the voltage at the DUT pin from the sense line to determine if the desired voltage is provided at the DUT. Here, assuming the force line (node 28) has a 1 ohm resistance and the power supply current IS is 1 A. The voltage VS at the DUT pin is actually only 4V due to the voltage drop on the force line. The sensed voltage VS is fed back to the power supply Supply-K and the power supply, such as through amplifier 25, drives the force line until the sensed voltage VS at the DUT is the same as the programmed voltage VSK. To ensure driving and sensing operation at the tester, the force-and-sense pair connection between the tester and the DUT should not be broken or the tester will not be able to measure the voltage at the DUT correctly.